Home > Articles > Networking > Storage

This chapter is from the book

This chapter is from the book

Switches

Fibre Channel switches are one of the most powerful components of a SAN. They are responsible for the efficient and high-speed switching of frames over a storage network. These switches are the basis of the switched Fabric topology, where the switches are interconnected to form the Fabric. The Fabric, in turn, can support numerous point-to-point connections, individual nodes, and arbitrated loops.

Unlike Fibre Channel hubs that are generally used to implement the arbitrated loop topology and extend the effective distance of a loop, Fibre Channel switches offer enhanced and more complex functionality. As a part of the Fabric, Fibre Channel switches are responsible for the following:

  • Providing a dedicated bandwidth of 100 Mbps and higher per port. This means that all switch ports can engage in separate transactions simultaneously without affecting other transactions.

  • Providing high-speed switching of frames from source to destination ports.

  • Providing frame flow control during communication. Switches use services such as buffer-to-buffer credit for this purpose. Buffer-to-buffer credit, also known as BB_Credit, determines the maximum number of buffers available per port if buffer flow control is in use.

  • Providing Fabric services, such as Fabric login, Simple Name Server (SNS), State Change Notification (SCN), and Registered State Change Notification (RSCN).

    NOTE

    See Chapter 6 for more information about Fabric services.

A typical Fibre Channel switch offers 8 to 16 ports. Therefore, a single switch can successfully support a small-scale SAN. A small-scale SAN can consist of a few hubs, application servers, database servers, and high-performance storage devices. A small-scale SAN can also be extended effectively by cascading two or more switches. However, the larger the number of cascaded switches, the greater the possibility that the cascaded links can end up as bottlenecks in switch-to-switch transactions. In this case, redundant links might prove to be an effective solution as they provide an alternate path between Fabric switches.

Types of Switches

Fibre Channel switches are generally classified into three categories—loop switches, Fabric switches, and directors. Loop switches are the most cost-effective category of switches that are used to connect an FC-AL to the Fabric. They support full-duplex data transfers and are ideal for low-bandwidth devices. Mostly, they are implemented for connecting legacy loop devices to the Fabric and tape consolidation. Typically, most loop switches support eight ports.

Fabric switches offer a high-speed category of switches that form the Fibre Channel Fabric. They support full-duplex data transfers that are not affected by simultaneous communi-cations. They can efficiently support small SANs and act as the consolidation point of larger SANs. Fabric switches are generally implemented in SANs where storage devices are distributed geographically, such as storage wide-area networks (SWANs). A typical Fabric switch offers 16 to 32 ports.

Directors are a high-bandwidth, high-availability (99.999%), and high-performance category of switches that offer fully redundant, hot-pluggable components that can include processors and various switching elements. As a result, these switches are considered to be the most reliable. Their downtime is estimated to be about five minutes or less in a year. This makes them the most expensive category of switches. Directors are implemented in mission-critical and performance-intensive applications where downtime must be as low as possible. They are also used to implement the backbone for enterprise SANs. Directors offer 32 or more ports.

The price of switches can range from about $7500 to $45,000, depending on the function-ality provided by the switch. Many vendors offer Fabric switches. IBM, Vixel, Compaq, HP, Gadzoox, Brocade Communications, Inc., Hitachi, and McData are some of the most well-known vendors in the field of Fibre Channel switches.

Cisco Systems, Inc., offers the Catalyst 6000 and Catalyst 4000 family of switches for storage networking solutions. These switches are described in the following sections.

Catalyst 6000 Family Switches

The Catalyst 6000 family of switches is actually a set of Catalyst 6500 and Catalyst 6000 series of switches. These switches were designed to offer the following features that are extremely important in gigabit Fibre Channel networks:

  • Extensive intelligent network services

  • Exceptional scalability

  • Optimal price and performance

  • High availability

  • Support to a wide range of interfaces that are used in Fibre Channel networks

Figure 4-10 shows a Catalyst 6000 family switch.

Figure 4-10Figure 4-10 Catalyst 6000 Family Switch

The functionality of members of this family include the following:

  • High performance—The Catalyst 6513 switch from the Catalyst 6500 series offers switching speeds up to 210 million packets per second. The switch also offers 1152 10/100 and 388 gigabit ports per 7-inch rack.

  • Switch Fabric Module 2—The Catalyst 6500 family offers scalable switching bandwidth up to 256 Gbps, while ensuring the highest level of availability.

  • Content Switching Module (CSM)—The Catalyst 6000 and 6500 families offer CSM that helps in tracking network sessions and server load conditions in real-time. CSM also directs each session to the appropriate server.

  • Optical Services Modules (OSM)—The Catalyst 6500 series switches offer optical WAN interfaces, deep packet buffers, and PXF IP Services Processors for high-speed IP service applications.

  • Supervisor Engine 2—The Catalyst 6000 and 6500 families offer a CEF-based architecture, which helps in increasing the overall system performance to 100+ Mbps.

  • Cisco Express Forwarding (CEF)—The Catalyst 6500 family offers CEF, which in collaboration with Supervisor Engine 2 and Gigabit Ethernet Modules delivers next generation solutions for dynamic service provider and enterprise networks.

  • Gigabit Ethernet Switching Module—The Catalyst 6500 family offers Gigabit Ethernet Switching Modules that are ideal for gigabit backbones, server farms, and high-density wiring closets.

  • Intrusion Detection System (IDS)—The Catalyst 6000 family switches integrate switching and security functionality to provide comprehensive attack detection against unauthorized and malicious access.

  • Quality of service (QoS)—The Catalyst 6000 and 6500 families offer high QoS, high-availability, and security.

    NOTE

    For more information on Catalyst 6000 series switches, refer to the site www.cisco.com/warp/public/cc/pd/si/casi/ca6000.

Catalyst 4000 Family Switches

The Catalyst 4000 family of switches offers modular switches (Catalyst 4003 and Catalyst 4006) that are an integral part of Cisco's Architecture for Voice, Video, and Integrated Data (AVVID) solutions. AVVID offers scalable and manageable solutions for both SAN- and NAS-based networks.

The main features of the Catalyst 4000 family switches include the following:

  • IP access to storage

  • Support to multimedia traffic, such as IP telephony, unified messaging, and Virtual Private Networks (VPNs)

  • Scalability and future growth

    NOTE

    For more information on Catalyst 4000 series switches, refer to the site www.cisco.com/warp/public/cc/pd/si/casi/ca4000.

Figure 4-11 shows a Catalyst 4000 family switch.

Figure 4-11Figure 4-11 Catalyst 4000 Family Switch

Fibre Channel Switches Versus Hubs

While designing and implementing a storage network, one source of confusion is when to use hubs and when to implement switches. There are relevant considerations when deciding between hubs and switches including shared bandwidth, network population, services, security, and future growth. The following sections discuss these considerations.

Shared Bandwidth

Except for switched hubs, the bandwidth offered by managed and unmanaged hubs is shared. This means that if a 10-port hub offers 100 Mbps bandwidth, each individual hub port gets a bandwidth of only 10 Mbps. On the other hand, a 10-port 100 Mbps switch provides 100 Mbps bandwidth to each individual switch port.

Some applications, such as sustained full-motion video streams and streaming tape backups, are extremely sensitive to delays. As a result, hubs are not the right choice in storage environments where audio and video data is exchanged or tape backup data is streamed predominantly.

Network Population

The total number of nodes supported by the storage network also affects the choice of a hub or switch. If the number of nodes is smaller (5 to 40 nodes), hubs seem to be an ideal solution. However, for a large number of nodes (more than 100), switches are the best solution because the larger the network population, the greater the need of switching frames from source to destination. For networks that consist of 50–100 nodes, a mix of hubs and switches offers an optimal solution.

Services

In a large storage network populated with a large number of devices, discovering the required nodes or ports can be a tedious and complex task. Moreover, if a node goes down, other nodes might not know about the change in its status and try to contact it. This can result in long request queues for the failed node. Services, such as Fabric login, SCN, and RSCN, are very helpful in the quick and efficient discovery of the required disk, port, or node and their corresponding status. These services, however, are not obligatory, and nodes need to register themselves for notifications regarding changes in topology and individual device status.

The SCN service allows an N_Port to send a change notification to another N_Port that has registered its interest in any change of the given node or port. Therefore, only the port that was notified about the change would know about the change in status. The other members of the Fabric do not know about the change. RSCN offers a better solution to this problem. All the registered nodes are informed about the change simultaneously, thus allowing more than one node or port to know about the change. This helps in the fast discovery of the destination node or port.

Security

If security is a requirement in your storage network, it is advisable to use switches. This is because most of the hubs do not allow zoning, which is a common feature of Fibre Channel switches. Zoning prevents access to nodes or ports that do not belong to the same zone, thereby reducing the risk of unauthorized, malicious attacks to confidential corporate data.

Dynamic zoning also proves to be very helpful in networks where nodes (such as portable computers) are often physically relocated. Instead of moving hubs around and physically rewiring the entire setup, dynamic zoning allows the relocation of nodes without the need of physical rewiring. At the same time, the security setup is not affected.

Future Growth Potential

In a situation where the number of nodes in a storage network is small but is estimated to increase in the near future, switches prove to be an intelligent choice. Switches are highly scalable and have a higher potential for future growth. In contrast, scalability of hubs is limited because of shared bandwidth and security restrictions.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020